Creating multiple and discriminate images on the same plane is currently achieved by lenticular or holographic techniques. Lenticular techniques rely on the images being separated by a secondary sheet of lenses to discriminate the images. The images are interleaved together and a lenticular sheet composed of a series of cylindrical lenses molded into a plastic substrate is layered on top of the interlaced image.
Holograms or light interference is another way to discriminate images on the same recording plane. With holograms, the goal is to record the complete wave field of both amplitude and phase. In order to record the complete wave field of both amplitude and phase, a reference beam is created to interfere with the object of exposure and then recorded onto a recording medium several microns thick. However, this thickness can often pose an obstacle in terms of image recording time and versatility. For example, in a dot matrix hologram method described in European patent No. 91306316.0 as cited in U.S. Pat. No. 5,452,282, individual holographic gratings are produced by changing the alignment angle of the interference beam to expose from 255 discrete angles. This process is typically very slow and usually takes 5 to 6 hours to expose a one-inch square area.
Another technique, demonstrated by holography pioneers Emmett N. Leith and Juris Upatnieks, separates images using a reference beam that is recorded at a different angle from the object than the beam. However, like other holographic techniques, this relies on the interference pattern of two wavefronts, which causes difficulties and inaccuracies in terms of alignment and environmental controls.
With respect to optical storage media, U.S. Pat. No. 6,011,767 describes a method for providing holograms, wherein the holograms are created on the same surface as the digital recordings using successive exposures with different lasers to create phase interference. This method requires two light wave exposures that create phase interference diffraction gratings to create holograms or dot matrixed holograms. These phase interference diffraction gratings are uniform. Devices incorporating these uniform gratings are commonly referred to as Optical Variable Devices or OVD's. As such, under an Atomic Force Microscope (AFM), an OVD image has evenly distributed gratings and no discrete components. Additionally, creation of these uniform, phase interference diffraction gratings requires expensive and complex multi-laser hardware. This is very different from machines that create digital recordable, re-playable indentations that only use a single beam.